Process for preparing unsaturated polyester

ABSTRACT

An unsaturated polyester is prepared via an epoxide-anhydride process wherein the copolymerization occurs in the presence of a reactive diluent, initiator, mild catalyst and a free radical inhibitor at a temperature of 20*C. - 175*C.

United States Patent 1 1 3,723,573

Thompson 1 Mar. 27, 1973 [54] PROCESS FOR PREPARING 2,632,753 3/1953Anderson ..260/866 UNSATURA POLYESTER 2,822,350 2/ 1958 Hayes ..260/78.43,254,060 5/ 1966 Connolly et al. ..260/78.4 [75] Inventor: Robert M.Thompson, Wilmington, 3,374,208 3/1968 Seiner et al ..260/78.4 Del.3,375,301 3/1968 Case et a1. ..260/869 3,483,169 12/1969 Case et a1...260/78.4 [73] Asslgnee: Sun Research and Development Co.,

Philadelphia, Primary Examinerwilliam n. Short 22 Filed: No 11 1971Assistant Examiner-E. Nielsen Attorney-George L. Church et a1. [21]App]. No.: 197,983

52 US. Cl. ..260/866, 260/75 EP, 260/78.4 EP, [57] ABSTRACT 260/864 Anunsaturated polyester is prepared via an epoxide- [51] Int. Cl. ..C08f21/02, C08g 17/ 12 h dride process wherein the copolymerization oc-Field of Search 75 EP curs in the presence of a reactive diluent,initiator,

mild catalyst and a free radical inhibitor at a tempera- [56] ReferencesCited ture of 20C. 175C.

UNITED STATES PATENTS 9/ 1952 Anderson ..260/866 X 21 Claims, NoDrawings PROCESS FOR PREPARING UNSATURATED POLYESTER BACKGROUND OF THEINVENTION the presence of a catalyst and an initiator. At this temlperature, the isomerization of the maleate structure to the morereactive fumarate form is not favored unless a suitable catalyst isused. So, after the copolymerization is completed, post heating at 190C.230C. for 2 5 hours is performed to effect isomerization. After thecopolymerization is completed, the unsaturated polyester, in part,because of its high viscosity, is diluted with a reactive diluent, e.g.,styrene. This diluent also enters into a cross-linking reaction whichenhances the ultimate use product, e.g., a boat hull. Also to thediluted unsaturated polyester is added a free radical inhibitor toprevent the styrene from homopolymerizing. This process is described inUS Pat. No. 3,254,060, issued May 31, 1966.

The aforementioned diluent serves two functions: (1 adjusts theviscosity of the unsaturated polyester to the desired fluidity whichfacilitates ease of handling and (2) coreacts with the polyesterunsaturation to achieve rapid and complete final cure to a cross-linkedhigh strengthproduct. The reactive diluent is usually a vinyl monomer.An example of one used commercially in great quantities is styrene.Others are listed in EN- CYCLOPEDIA OF CHEMICAL TECHNOLOGY, Kirk-Othmer,2nd Edition, Vol. 20, section Unsaturated Polyesters. The addition of areactive diluent to the unsaturated polyester, such as styrene, createsa problem since the latter is very susceptible to homopolymerization.Styrene is known to be highly susceptible to homopolymerization,catalyzed by ionic or free radical systems. Styrene polymerization isalso known to be initiated thermally at a temperature as low as 60C.Also, the dilution of the unsaturated polyester with the reactivediluent required an extra processing step which is time consuming andrequires additional heating.

The thermosetting composition; i.e., the mixture of the unsaturatedpolyester and the reactive diluent, resulting from the aforementionedtypical epoxide-anhydride process can be cast or molded into a desiredshape. Other additives, such as a filler, colorant, mold and releaseagent, antioxidants, antistatic, flame retardants, ultravioletstabilizers, etc. can be incorporated into the thermosetting compositionprior to the application of heat and/or catalyst to convert the liquidto a solid. Methods of forming desired polyester shapes, as well as thevarious additives and conversion catalysts, are described in theaforementioned encyclopedia.

The finished thermosettable product is shaped by fabricators. Themethods of fabrication include compression or match-metal die molded,laminated, pultruded, filament wound, transfer molded, bag molded, drapemolded, sprayed-up, hand layed up and cast. These fabrication methodsare defined in the trade literature, for example, MODERN PLASTICS EN-CYCLOPEDIA, 1970/1971, page 194. Since most of these applications forunsaturated polyesters require rapid conversion from a liquid to acompletely cured solid state, it is necessary to accelerate the cure bythe addition of unstable substances that produce free radicals and/orheating the mixture or some other means of generating free radicals.Curing refers to the final cross-polymerization of the unsaturatedpolyester with the reactive diluent, the latter being the cross-linksbetween the ester molecules.

SUMMARY OF THE INVENTION Present epoxide-anhydride process relates tothe preparation of an unsaturated polyester by a copolymerizationreaction taking place in contact with a reactive diluent, mild catalyst,an initiator, and free radical inhibitor at a temperature of about 20C.C. without substantial polymerization of the reactive diluent. Thisone-step copolymerization method avoids the time and heat consuming stepof the conventional practice of subsequently diluting the viscousunsaturated polyester with the reactive diluent. Operable amounts ofreactants, diluent, catalyst and other materials are specified.

DESCRIPTION In the preparation of an unsaturated polyester via theepoxide-anhydride method defined herein, three reactants arecopolymerized. One of the reactants is an anhydride of an ethylenicallyunsaturated dicarboxylic acid or a mixture of such anhydrides. Anotherreactant is an anhydride of an alkylene or arylene dicarboxylic acid ora mixture of such anhydrides. The third reactant is an epoxide or amixture of epoxides.

The anhydride of an ethylenically unsaturated dicarboxylic acid refersto a reactant which can be represented by the following structure:

wherein each of R, and R can be H or an organic radical containing 1 20carbon atoms. Preferably, each of R and R, is an H or an alkyl radicalcontaining 1 10 carbon atoms and more preferably, each of R and R is anH or alkyl radical containing 1 5 carbon atoms. When R and R are H, thenthe reactant is maleic anhydride which is highly preferred.

The anhydride of an alkylene dicarboxylic acid refers to a reactantwhich can be represented by the following structure:

wherein n 2 to 20. A few examples are succinic, glutaric and adipicanhydrides. Alkylene dicarboxylic anhydrides wherein n 2 to 5 arepreferred.

The anhydride of an arylene dicarboxylic acid refers to a reactant whichcan be represented by the following structure:

wherein each of R R R and R, is an H or an organic radical containing 120 carbon atoms. Preferably, at least three of the aforementioned Rs areHs and the remaining R is H or an organic radical containing 1 10 carbonatoms; more preferably the remaining R is H or an alkyl radicalcontaining 1 5 carbon atoms. When the four R's are H, the resultingreactant is phthalicanhydride which is highly preferred.

The third reactant is anepoxide which is a material incorporating athree membered ring containing one oxygen atom and two carbon atoms,i.e.,

The simplest member of the series is ethylene oxide. While propyleneoxide is the preferable epoxide, other epoxides such as ethylene oxideand butylene oxide can be substituted therefore in whole or in part.Other epoxides can be used such as styrene oxide and a methyl styreneoxide.

The operable amounts of the three aforementioned reactants in contactwith each other are as follows. The mole ratio of (A), a substanceselected from the group consisting of an anhydride of an ethylenicallyunsaturated dicarboxylic acid and a mixture of said anhydrides, to(B),'a substance selected from the group consisting of anhydride ofalkylene dicarboxylic acid, mixture of said alkylene anhydride,anhydride of arylene dicarboxylic acid, mixture of said alkyleneanhydrides and a mixture of said alkylene and arylene anhydride, is inthe range of about 0.7 1.5. A preferable range is about 0.9 1.25 andmore preferable is about 0.95 1.1. The mole ratio of (C), a substanceselected from the group consisting of epoxide and mixture of epoxides,to (A) plus (B), is about 0.8 1.2; a preferable range is about 0.9 1.1.

The aforementioned reactants are brought together, along with othermaterials described hereinafter, at an operable temperature of about20C. 175C; a preferable range is about 30C. 150C.

While these reactants will copolymerize without a catalyst, the rate ofreaction is rather slow for commercial use. Thus these reactants arebrought together in the presence of a catalyst selected from the groupconsisting of alkali metal salts, alkaline earth metal salts and saltsof organic amines. This group of catalyst is referred to herein as amild catalyst; this contrasts it with strong catalyst which refers toalkali metal hydroxides, alkaline earth metal hydroxides and hydroxidesof organic amines.

ln practicing the present invention, the aforementioned mild catalysts.are operable; preferable mild catalysts are the chlorides and bromidesof Group I and I1 elements. The weight ratio of catalyst that can beemployed to weight of the reaction mixture is about 0.01 5, preferably0.05 2.5.

ln addition to the aforementioned catalyst, an initiator must beincluded in the reaction mass. The initiator helps in getting thereaction started and acts to regulate the molecular weight of theresulting unsaturated polyester. The initiator can be a hydroxylcontaining substance such as water, alcohol and glycol. The amount ofinitiator employed with reaction mass depends, in part, upon the desiredmolecular weight, however, the typical mole ratio of initiator toreactants is 0.01 0.10, with 0.02 0.08 preferred.

The molecular weight of the resulting unsaturated polyester can be aslow as 200 or as high as 800 5,000. Too low a molecular weight increasesthe curing time of the thermosettable product, while too high amolecular weight, which causes the thermosettable product to have a highviscosity, causes handling problems for the ultimate fabricator. Thus amore desirable molecular weight range is about 1,000 3,000.

Surprisingly, it has been found that the reactants as defined herein canbe copolymerized to an unsaturated polyester in the presence of thereactive diluent with only a minimal amount of reactive diluenthomopolymerization or cross-linking. Thus, for example, it is possibleto form an unsaturated polyester from propylene oxide, maleic anhydrideand phthalic anhydride in the presence of styrene without seriouslyaffecting the properties of cured product.

In practicing the present invention, the mole ratio of reactive diluentto the aforementioned reactant (A) is in the range of about 2 3; apreferable range is about 2.25 2.75.

To minimize the homopolymerization of the susceptible reactive diluent,a free radical inhibitor is also added to the reaction mixture. In thetypical processing sequence, such an inhibitor would be incorporated,along with the reactive diluent, with the unsaturated polyester afterthe reactants had copolymerized. However, in the present invention, theinhibitor is added, along with the reactive diluent, to the reactionmixture before the copolymerization has taken place.

One example of a class of free radical inhibitors are the quinones;benzoquinone being particularly effective. These free radical inhibitorsare discussed in greater detail in the aforementioned encyclopedia.

The amount of free radical inhibitor used depends on the amount of thereactants and other components. The weight of free radical inhibitor tothe weight of (A) plus (B) plus (C) plus initiator plus reactive diluentplus catalyst is in the range of about 0.01 0.20; preferably 0.02 0.10.

The present inventioncan be practiced in either a batch or continuousprocess; the former being preferred.

After the aforementioned reactants, mild catalyst, initiator, reactivediluent and free radical inhibitor have been contacted at 20C. 175C.until the desired molecular weight has been obtained, the resultingfinished thermosettable product can be used immediately or cooled andstored until needed or shipped from the producer to the fabricator.

The curing of the thermosettable product is effected by the applicationof heat and/or pressure in the presence of a free radical yieldingcatalyst. Catalysts that may be used for the curing or polymerizationare preferably the peroxide catalysts such as benzoyl peroxide, lauroylperoxide, t-butyl hydroperoxide, methyl ethyl ketone peroxide, t-butylperbenzoate, potassium persulfate, 2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane and the like. The amount of the catalyst addedwill vary preferably from 0.1 percent to about 5 percent by weight ofreactants. Temperatures employed may vary over a'considerable range butusually are in the range of 40C. 150C.

Additionally, more rapid curing of the thermosetting resin compositionsmay be accomplished by the addition of accelerating agents such as leador cobalt naphthenate, dimethyl aniline and the like usually inconcentrations ranging from 0.1 5.0 weight percent.

In order to further illustrate the invention, the following example isgiven, along with comparative runs.

EXAMPLES The results of eight runs are reported in the accompanyingTables I and II. Runs 1 and 2 were comparative runs wherein thecopolymerization did not take place in the presence of a reactivediluent. In Runs 3 8, the copolymerization took place in the presence ofa reactive diluent. Run 8 is an example of the invention. Runs 3 7, bycomparison with Run 8, indicate the criticality of the amounts of thereactants and other materials used in Run 8.

The general procedure for preparing the unsaturated polyester of Runs 38, shown in the accompanying Tables I and II, was as follows. In Run 3 aone liter Parr reactor equipped with a low shear stirrer; i.c., a slowpaddle stirrer, after being pressure tested, was charged with 0.87 grammoles of maleic anhydride, 1.93 gram moles of phthalic anhydride, 0.22gram moles of propylene glycol, l.l grams of lithium chloride, 0.013gram moles of benzoquinone and 1.3 gram moles of styrene. The reactorwas purged of air by pressurizing with 40 psig nitrogen three times.After the last pressurizing, the pressure of the reactor was reduced to4 psig and then 1.5 gram moles of propylene oxide were charged through aJergensen gauge under 10 psig pressure. Afterwards, the reactor waspressurized with nitrogen to 40 psig and then heated to a temperature of90C. and maintained at that temperature for 6 hours. During the 6 hours,the reaction mixture was continuously stirred. The reaction was followedby the changes in apparent acid number of withdrawn samples of thereaction mixture.

Thus, for example, the apparent acid number of Run 3 changed with timeas shown hereinafter:

Time Apparent Acid No.

3.0 hours 68 4.0 hours 58 5.5 hours 49 6.0 hours 48 Since only a smallchange occurred in the apparent acid number during the last half anhour, the reaction was about completed and thus the heat discontinued.The reaction mixture was poured hot into a container and stored undernitrogen until cooled.

Apparent acid number measurement indicates the amount of polymerizationand can be used to follow the reaction as it proceeds. The commerciallyacceptable acid range is about 20 50.

Also shown in Table I, under Item 2, Copolymerization Conditions, is G HVis. This is a viscosity measurement which reflects molecular weight ofunsaturated polyesters at a specified concentration of monomer. Theunsaturated polyester solutions are compared with a series of viscositystandards assigned a letter and increasing from A Z. then Z-l to Z-6.The G l-I viscosities usually obtained for unsaturated polyester estersdissolved in 30 mole percent styrene range from Z-l to Z-3. Severalruns; namely, 1 and 2, were made for comparison of operating conditionsand physical properties of the cured polyester. The procedure for Runs 1and 2 was different in that in Run 1 no reactive diluent was present inthe reactor during the copolymerization. Also, after Run 1 was completedand about half of the reaction mixture was removed from the reactor, theremaining reaction mixture was heated to the higher temperature shown inTable l for The general procedure for curing the unsaturated polyestersof Runs 1 7, shown in Table I, was as follows. The specified amount ofcure catalyst was dissolved in the unsaturated polyester-styrenesolution. In some cases this required first warming the solution. Theresulting solution was poured into molds made from stainless steelplates, 3 X 5 inches using a A inch spacer and a C clamp was used tohold them together. Cellophane was used as a mold release. The moldswere cured in an oven at 55C. for 16 hours and then the temperature wasincreased over 30 minutes to C., after which it was maintained at thattime for 2 hours. The molds were removed from the oven and allowed tocool. Subsequently, the molded cured polyester was subjected to thevarious physical tests shown in Table I.

Comparison of the physical properties of the cured polyester product ofRuns 1 and 2 illustrated the improvement caused by post heating toeffect isomerization of the maleate structure. Thus, in Run 1, the curedpolyester was too brittle to measure its hardness, whereas the curedpolyester of Run 2 had a satisfactory hardness.

The physical properties of the cured polyester products of Runs 3 7 wereunsatisfactory in comparison to the product of Run 2.

Flexurul modulus", M p.s.i

Gram moles.

B l )A =benzyldimethylaminc.

c TMAB tctramethylammonium bromide.

4 BP=benzoyl peroxide, MEK=methylethyl ketone peroxide. G=clear,1)=opaque, T=translucent. TB=too brittle; the larger the number, I;TS=too soft.

* Molecular weight, calculated from initiator concentration. i Mg.KOll/g. sample.

i Low molecular weight polyester.

'lAli Ll'l I Operating conditions used to prepare unsaturated polyestersRuns [\lntvrinls :nul conditions 1 2 3 l 5 h 7 h l. ltezu'tnntszPropylene oxideuflu 1.53 .5 1.33 2.5 2.3 23.8 2.8 2. lnitinloi'zPropylene glycol. 0.35 J. 0. 22 0 175 0.175 0.175 0. l75 3. (hitnLyst,grains:

LiUl 1.1 1 LI 1 1 DNA n. 0.1

TMAUQ l .r 0.1 A H 4. Free radical inhibitor: Benzoquinone V V .7 0.0135. Reactive dilnentz' Styrene 1. 3 (i. Copolymerizntion conditions Time,hours 3 6 6 Acid N05. 30 2.) '10 1 colors V 16-17 0-1 4-5 MN calc." V A1,560 1,630 1,37 7. Cured polyester product:

Cure catalyst and wt. percent L. Bll3 BP/B B 1/3 llP/3 Clarity C C U '1Extruetables, \vt. percent 2. 8 16 5 Flexurul strength, p.s.i TS TS thebetter product, satisfactory cured polyesters have range of -55.

k Weight percent; i.e., weight of inhibitor to weight of reactants plusinitiator plus reactive diluent.

1 See Table I1. 2 Run 2 is material from Run 1 after completion of Run1.

TABLE 11 [Comparison of cured polyester products] Material made from viathe usual polycsterficotion process. b2,5-dimcthyl-2,5-l)is(2-ethylhoxanoylperoxy) hexane.

The invention claimed is: l. A process for the preparing of anunsaturated polyester comprising:

contacting together at a temperature of about 20C. 175C. the following:(A) a substance selected from the group consisting of an anhydride of anethylcnically unsaturated dicarboxylic acid and a mixture of saidanhydrides; (B) a substance selected from the group consisting ofanhydride of alkylcne dicarboxylic acid, mixture of said alkyleneanhydrides, anhydride of arylene dicarboxylic acid, mixture of saidarylcne anhydridcs and a mixture of said alkylene and arylenc anhydridc;and (C) a substance selected from the group consisting of epoxide andmixture of epoxides;

said contacting occurring in the presence of a mild catalyst selectedfrom the group consisting of alkali metal salts, alkaline earth metalsalts, and salts of organic amines, an initiator, a reactive diluentwhichis a vinyl monomer, and a free radical inhibitor;

and thereafter agitating said contacting materials at said temperatureuntil a desired molecular weight is obtained;

the amounts of (A) and (B) being such that the mole ratio of (A) to (B)is about 0.7 1.5; the amount of (C) being such that the mole ratio of(C) to (A) plus (B) is about 0.8 1.2; the amount of reactive diluentbeing such that the mole ratio of said diluent to (A) is about 2 3; theamount of free radical inhibitor being such that the weight of saidinhibitor to weight of (A) plus (B) plus (C) plus initiator plusreactive diluent plus catalyst is about 0.01 .20; the amount of catalystbeing such that the weight ratio of said catalyst to the reactionmixture is about,0.0l 5.0; and, the amount of initiator being such thatthe mole ratio of initiator to (A) plus (B) plus (C) is about .01 0.10.2. Method according to claim 1 wherein the ratio of (A) to (B) is about0.9 1.25.

3. Method according to claim 1 wherein the ratio of (C) to (A) plus (B)is about 0.9 1.1.

4. Method according to claim 1 wherein the ratio of reactive diluent to(A) is about 2.25 2.75.

5. Method according to claim 1 wherein the temperature is about 30c. C.

6. Method according to claim 1 wherein the reactive diluent is styrene.u

Method according to claim 1 wherein the free radical inhibitor is aquinone.

8. Method according to claim 1 wherein the mild catalyst is one of thefollowing: chloridcof Group I element, chloride of Group II element,bromide of Group 1 element and bromide of Group II element.

9. Method according to claim 1 wherein the initiator is a glycol.

10. Method according to claim 1 wherein the molecular weight of theunsaturated polyester is 200 5,000.

11. Method according to claim 2 wherein (A) is maleic anhydride.

12. Method according to claim 11 wherein (B) is phthalic anhydridc.

13. Method according to claim 3 wherein (C) is propylene oxide.

14. Method according to claim 4 wherein the reactive diluent is styrene.

15. Method according to claim 5 wherein the ratio of 5 (A) to (B) isabout 0.9 1.25; the ratio of (C) to (A) plus (B) is about 0.9 l.l; theratio of reactive diluent to (A) is about 2.25 2.75 and weight ofinhibitor is about 0.02 0.10.

16. Method according to claim wherein the free radical inhibitor is aquinone; the mild catalyst is one of the following: chloride of Group Ielement, chloride of Group II element, bromide of Group I element,bromide of Group [I element; and the initiator is a glycol.

2. Method according to claim 1 wherein the ratio of (A) to (B) is about0.9 - 1.25.
 3. Method according to claim 1 wherein the ratio of (C) to(A) plus (B) is about 0.9 - 1.1.
 4. Method according to claim 1 whereinthe ratio of reactive diluent to (A) is about 2.25 - 2.75.
 5. Methodaccording to claim 1 wherein the temperature is about 30*c. - 150*C. 6.Method according to claim 1 wherein the reactive diluent is styrene. 7.Method according to claim 1 wherein the free radical inhibitor is aquinone.
 8. Method according to claim 1 wherein the mild catalyst is oneof the following: chloride of Group I element, chloride of Group IIelement, bromide of Group I element and bromide of Group II element. 9.Method according to claim 1 wherein the initiator is a glycol. 10.Method according to claim 1 wherein the molecular weight of theunsaturated polyester is 200 - 5,000.
 11. Method according to claim 2wherein (A) is maleic anhydride.
 12. Method according to claim 11wherein (B) is phthalic anhydride.
 13. Method according to claim 3wherein (C) is propylene oxide.
 14. Method according to claim 4 whereinthe reactive diluent is styrene.
 15. Method according to claim 5 whereinthe ratio of (A) to (B) is about 0.9 - 1.25; the ratio of (C) to (A)plus (B) is about 0.9 - 1.1; the ratio of reactive diluent to (A) isabout 2.25 -2.75 and weight of inhibitor is about 0.02 - 0.10. 16.Method according to claim 15 wherein the free radical inhibitor is aquinone; the mild catalyst is one of the following: chloride of Group Ielement, chloride of Group II element, bromide of Group I element,bromide of Group II element; and the initiator is a glycol.
 17. Methodaccording to claim 16 wherein (A) is maleic anhydride, (B) is phthalicanhydride, (C) is propylene oxide and the reactive diluent is styrene.18. Method according to claim 17 wherein the quinone is benzoquinone,the mild catalyst is lithium chloride, and the glycol is propyleneglycol.
 19. MethOd according to claim 18 wherein the method is a batchprocess.
 20. Method according to claim 19 wherein the molecular weightof the unsaturated polyester is 1,000 - 3,000.
 21. Method according toclaim 19 wherein the method is a continuous process.